A nationwide ceasefire between Syrian government forces and rebel groups has come into effect.
The truce, brokered by Russia and Turkey, which will act as guarantors, began at midnight (22:00 GMT).
The deal includes a large number of rebel groups but not jihadists such as the so-called Islamic State, or the Kurdish YPG.
If the ceasefire holds, peace talks are scheduled to be held in Kazakhstan within a month.
At least 300,000 people are believed to have been killed in fighting that followed the uprising against President Bashar al-Assad in March 2011.
A further four million have sought refuge in neighbouring states or Europe.
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Why is there a war in Syria?
Will the ceasefire hold?
The diplomatic noises are encouraging, and even the rebel groups involved have suggested it could succeed.
However, previous ceasefire initiatives this year brokered by the UN, or the US acting with Russia, quickly collapsed.
The Kremlin said President Vladimir Putin had spoken to Bashar al-Assad and that the Syrian leader had said he was “committed to implementing” the agreement.
Syrian Foreign Minister Walid Muallem said there was “a real chance to reach a political settlement to end the bloodshed and establish the future of the country”.
The fact that the rebels have been losing ground may help.
The High Negotiations Committee (HNC), the umbrella group representing Syria’s political and armed opposition factions, admitted on Thursday that, because of the rebels’ limited resources, it was “not possible to continue” the fight.
One rebel commander told Reuters news agency: “This time I have confidence in its seriousness. There is new international input.”
Who is included in the ceasefire deal?
On the one side, Syrian government forces, their factional allies and the Russian military.
On the other, the Free Syrian Army (FSA), a loose alliance of several moderate rebel factions, plus other groups under the HNC. FSA spokesman Osama Abu Zaid said there were 13 armed opposition factions in all who had signed up.
The Russian defence ministry listed seven of the main rebel groups included in the truce as Faylaq al-Sham; Ahrar al-Sham; Jaysh al-Islam; Thuwwar Ahl al-Sham; Jaysh al-Mujahidin; Jaysh Idlib and al-Jabhah al-Shamiyah.
Ahrar al-Sham and Jaysh al-Islam (Army of Islam) are the key names, neither of them part of the FSA.
However, reflecting the confusion of the Syrian conflict, Reuters later quoted one spokesman for Ahrar al-Sham as saying that the group had reservations and had not signed the deal.
Who is not included?
Jihadists. So-called Islamic State (IS) “and the groups affiliated to them” are not part of the agreement, Syria’s army confirmed.
It also said Jabhat Fateh al-Sham (formerly the Nusra Front) was excluded. However, some rebel officials told Reuters it was included in the deal, giving a hint of the complications that lie ahead.
This is because JFS is intrinsically linked in Idlib province to groups that have signed up to the truce.
The FSA also said that the deal did not include the Kurdish Popular Protection Units (YPG).
The YPG, along with other Kurdish militias, controls a large area of northern Syria up the Turkish border. It is regarded by Turkey as a terrorist organisation and an extension of the banned Kurdistan Workers’ Party (PKK).
Turkey’s PM Binali Yildirim later confirmed that “no group that we regard as a terror organisation will sit around the negotiating table”.
What are the terms of the deal and where does it cover?
It is nominally nationwide, although that really only covers the areas where the sides who have signed up to the truce have a presence.
Looking at the map, there are large swathes under both jihadist and Kurdish control.
One area that is included is the rebel-held area of Ghouta in eastern Damascus, where government forces have been advancing in recent months.
Announcing the deal in Moscow, Mr Putin said there were three key points:
- Ceasefire between the two sides
- Measures for overseeing the truce
- An agreement to start peace talks
Under the terms of the deal, the peace talks would begin within a month of the ceasefire taking effect – and holding – and would be held in the capital of Kazakhstan, Astana.
What has the international reaction been?
Turkish President Recep Tayyip Erdogan said a “window of opportunity” had been created that “should not be wasted”. He vowed to continue fighting IS and “terrorist groups”.
UN envoy for Syria, Staffan de Mistura, said he hoped the deal would save lives and improve aid delivery.
“These developments should contribute to inclusive and productive intra-Syrian negotiations to be convened under UN auspices on 8 February,” he said.
The US state department said the deal was a “positive development” which it hoped would be “implemented and fully respected by all parties”.
Are Turkey and Russia now allies?
On 24 November 2015, Turkey shot down a Russian warplane on its border with Syria and a big diplomatic freeze ensued.
But tough Russian economic sanctions – and Turkey’s increasing frustration with its Nato allies – led to a gradual thawing over 2016.
Turkey even turned a blind eye to the advance of Syrian forces on Aleppo and now the pair have brokered a truce.
There were even reports on Thursday that Russian aircraft had bombed IS targets near al-Bab – where Turkish troops are encircling the jihadists – shortly after President Erdogan had complained about the lack of Nato air support.
Still, problems remain. The sides have not spelled out jointly which rebel groups they believe are involved in the truce.
Turkey also says foreign fighter groups, including Hezbollah, need to leave Syria. This will not sit well with Iran, a major backer of the Assad government.
And it is unclear whether Ankara is prepared to give up on its long-term goal of ousting Mr Assad.